The present invention relates to a new and useful arrangement for extending the period between substantial maintenance required regularly for the shaft seals of rotary or linear moving shafts, such as valve stems, or other devices where the shaft extends into a fluid containing device, such as a valve body or a tank, and where the seal between the shaft and the outside is provided by means of compressible packing, all as known in the art.
Previous arrangements have typically required that the packing be periodically removed, and replaced with new packing inasmuch as the packing deteriorates for numerous reasons including age, heat, hardening, or other characteristic factors. Typically, the inconvenience occasioned by the failure of the packing around a shaft, for example a valve stem, depends upon the application of the device associated with the seal. For example, in some instances there is little or no inconvenience in shutting down a pipe line in order to replace the packing in a valve. In other arrangements the packing around a valve stem can be allowed to leak for an extended period of time without any substantial damage. However, in other applications, for example valve members utilized on high pressure steam headers, very little leakage can be tolerated because leakage almost immediately leads to failure of the valve and an inconvenient and sometimes dangerous shut down of the associated equipment. In the case of a high pressure steam header, the leak can shut down the entire plant or cause a power outage over an extended area.
The epitome of inconvenience is reached in nuclear power plants where in certain areas, for example areas where nuclear radiation is present, any leakage around valve stems can not be tolerated.
As previously stated, and as a general rule, all packing eventually leaks so the effectiveness of a particular seal arrangement is determined by the period of time which passes between leaks of a substantial nature requiring a shut down of the associated equipment. Accordingly, means to extend the period of time between shut-down of equipment for complete repair of valve seals is of particular importance in the economics of the operation of certain types of equipment, particularly nuclear power facilities.
Very few prior art means are known for extending the life of the packing provided around a rotatable shaft, for example a valve stem.
One such means for extending the life is a process provided by the Furmanite Corporation, wherein the valve housing is taped and a sealant pumped into the packing gland to provide an improved seal between the packing all ready in the housing and the stem. This process generally can be utilized only a few times before it is necessary to discard valve or the associated sealing equipment.
No prior art arrangement is known which permits the attachment of an alternate seal device to an existing seal device where the alternate device remains out of use and of no effect in the operation of the associated seal until such time as a leak develops in the packing gland initially provided for the shaft.